Synthesis And Characterization Of Ⅱ-Ⅵ Quantum Dots

This research mainly focused on the synthesis and characterization ofâ…¡-â…¥quantum dots in water. There are two parts needed to be studied in the synthesis ofâ…¡-â…¥quantum dots (QDs) and the toxicity of QDs in vitro.â…¡-â…¥Colloidal semiconductor nanocrystals (often known as quantum dots) have been attracted wide interests from biological and medical fields when used as fluorescent labels due to their unique and fascinating optical properties, such as sharp and symmetrical emission spectra, high quantum yield, good photo- and chemical stability, and size-dependent emission wavelength tenability. Most of the quantum dots used in biolabeling are synthesized in an organic phase by using high-boiling-point solvents such as trioctylphosphine (TOP) or trioctylphosphine (TOPO). However, these nanocrystals are generally capped with hydrophobic ligands which need further ligands exchange. In recent years, methods of preparing luminescent quantum dots in an aqueous phase have been significantly improved. Nevertheless, the study for toxicity of quantum dots is needed.In this paper, we used water as the solution to synthesize CdSe and CdTe quantum dots.In chapterâ… , the author briefly discusses the characteristics, synthesis, applications and toxicity of quantum dots.In chapterâ…¡, the author focuses on the aqueous synthesis conditions of CdSe and CdTe nanocrystals, and draws the conclusion that the ratio, the pH value, the capping reagent and the reaction time significantly affected the photoluminescence intensity and the stability of quantum dots. The proper molar ratio of Cd²⁺, E (Se or Te) and capping reagent should be 2: 1: 4～5. With the decreasing of the pH value, the growing rate of quantum dots decreasees dramatically. Using different capping reagents, the stability and the photoluminescence are different. The TGA and GSH capped QDs show good stability and can be stored for more than 100 days without any precipitation. The reaction time control the emission peak's position, which means with the time increasing, the size of QDs is growing slowly or sharply depending on the pH value.In chapterâ…¢, the author discusses the mercaptoethylamine capped CdSe toxicity in vitro. Exposure to QDs can lead to potential risks, which stem from the metallic component (Cd), the high surface-area-to-volume ratio and small size. Cell morphology observation and MTT assay show that quantum dots have much toxicity and show dose response.As a whole, we got different capped and size tunableâ…¡-â…¥quantum dots.